The objective of this proposal is to study the changes in microbial composition of dental plaque during its longitudinal development and to determine some of the principles which may govern these changes. In the first phase, the predominant cultivable microorganisms present in plaques of differing ages from a single site in the mouth of a single individual will be characterized and where possible identified. These organisms will be tested for their ability to form in vitro plaque, to adhere to enamel powder, and saliva-coated enamel powder, to agglutinate in the presence of saliva, and to agglutinate with other microorganisms present in the same sample at the same time. The effect of some of the isolated organisms on the oxidation reduction potential of their environment will be determined. Organisms which can markedly reduce their environment as well as organisms which can grow only in highly reduced environments will be characterized and the nature of their interrelationships studied. In addition the phenomenon of "suspected pairs" of microorganisms will be investigated in order to determine if these "pairs" are held together by intimate adhesion of the cells, are nutritionally interdependent or whether they represent marked variation of pure cultures. In later phases, the development of the gingival crevice microbiota on the same tooth of the same individual will be studied as outlined above. The microbiota of these two sites will be compared to each other and to two of the potential sources of the organisms namely the overlying cheek and the saliva bathing the areas. Developing plaque in other individuals in the same or different sites will also be examined.